Peel and chop your onion. Heat the oil in a large pot on medium-high. Add the onions to the pot and stir to coat them with oil. Cook the onions for five minutes or until they're soft, stirring occasionally to prevent sticking. While the onions are cooking, you can grate your cheeses if needed.
Add the frozen peas, salt and pepper to the pot and stir to combine. Let the peas cook for five minutes, stirring occasionally. They should be almost fully cooked.
Add your water to the pot and increase the heat to high. Cover the pot with a lid and let the water come to a boil. When the water is boiling, add your pasta and stir it to prevent sticking. Lower the heat slightly and cook the pasta until it's al dente, stirring frequently to prevent sticking, making sure to scrape the bottom of the pot. When the pasta is cooked, do NOT drain the water.
Turn off the heat and stir in your Parmesan and Romano. Taste to see if you need any extra salt. (You may not, since the Romano is salty.)
Serve with extra Parmesan (or Romano) and red pepper flakes at the table. Store leftovers in the refrigerator for up to five days.
I like to use a white onion here, since it's more mild than the yellow or red ones.
I always use baby peas, since they're more sweet than regular peas.
If you want to make this with meat, you can add chopped bacon or pancetta when the onions are soft. Use 3 strips of thick bacon or 4 strips of thin bacon.
Use boxed pasta for this recipe. We haven't tested it with homemade pasta, which cooks much faster and may not provide enough time for the water to absorb.